Reverse Boudouard Reaction Research Articles

Effect of nickle on cerium oxide support to develop cyclic catalytic methane decomposition followed by CO2 gasification

Catalytic methane decomposition (CMD) offers an eco-friendly method to produce COx-free hydrogen and solid carbon. An innovative approach for catalyst regeneration involves utilizing CO2 as a reactant to produce CO via the Reverse Boudouard Reaction, which serves as a valuable feedstock for various chemicals and fuels. This study aims to investigate the role and interaction of Ni nanoparticles on cerium oxide support by comparing two catalysts: one synthesized via the conventional impregnation method (Imp) and the other through solution combustion synthesis (SCS). Both catalysts containing the same Ni loading of 5 wt% and were tested under identical conditions. Comprehensive characterization techniques, including XRD, H2 and O2 TPR, TEM, SEM, XPS, and Raman spectroscopy, were employed to elucidate the observed performances. The SCS catalyst resulted in smaller Ni nanoparticles with stronger metal-support interaction. Observations revealed both tip and base carbon growth for the SCS catalyst, whereas the Imp catalyst predominantly characterized by tip growth. For the SCS catalyst, carbon nanofibers and nanotubes were observed, and both appeared active in carbon CO2 gasification. For the Imp catalyst, more crystalline carbon is observed. The amount of carbon produced was much more and managed to cover the entire catalyst. For SCS carbon coverage was partial. Two rates of CO2 gasification were observed depending on the extent of carbon coverage. Across all tested temperatures and space velocities, the catalyst prepared by impregnation exhibited higher reaction rates. The Imp catalyst demonstrated 15 % higher CMD and 29 % more generated carbon than SCS. This work demonstrated the critical role of key factors influencing the catalytic performance of this cyclic process. This includes the Ni nanoparticle size and distribution, the metal-support interaction's strength, and the graphitic carbon's nature.

Calcium looping-enhanced biomass gasification for methanol production: Integrating methane dry reforming and carbon utilization

Developing integrated CO2 capture and utilization (ICCU) is an attractive strategy that aims to reduce CO2 emissions while realizing the potential benefits of CO2. This paper investigates the techno-environmental-economic performance of biomass gasification to methanol (BtM) based on calcium looping (CaL) coupled with dry reforming of methane (DRM) and CaL coupled with reverse Boudouard reaction (RB). The results indicate that BtM systems based on CaL-DRM (BtM:CaL-DRM) and CaL-RB (BtM:CaL-RB) achieve CO2 capture and utilization, and enable efficient methanol synthesis. Compared to BtM:CaL-DRM, BtM:CaL-RB demonstrates higher exergy efficiency and lower global warming potential (GWP). The exergy efficiency of BtM:CaL-RB reaches 71.60 %. In terms of economic viability, BtM:CaL-DRM demonstrates more promising economic feasibility. The BtM systems reaches breakeven when the methanol selling price ranges from 440.8 $/ton to 529 $/ton. This study provides valuable insights into exploring novel ICCU systems.

Modeling of Fluidized Bed Molten Carbonate Direct Carbon Fuel Cell: Effect of Reverse Boudouard Reaction

Direct carbon fuel cells (DCFCs) are an alternative technology to coal-fired power plants for converting the chemical energy of abundant carbon-rich fuel into electrical energy. DCFCs have higher electrical efficiency and lower greenhouse emissions, which are easier to separate and capture. In the transition to renewable sources of energy, efficient and low-emission technologies need to be explored. Since DCFC technologies are in their early stages of development, modeling and simulation studies are needed to reduce costs and aid in experimental design. In this study, an electrochemical and transport model for a fluidized bed molten carbonate DCFC (FBMCDCFC) is developed. The performance of the fuel cell is evaluated through the polarization losses. This study expounds on recent developments in DCFCs by considering the effect of the reverse Boudouard reaction and the 2-electron oxidation of CO alongside the 4-electron oxidation of carbon at higher temperatures. The electrolyte used is a 62 : 38 mol % Li2CO3/K2CO3 eutectic mixture, while the fuel is activated carbon impregnated by HNO3. The results show that the greatest polarization losses for the FBMCDCFC are from anode activation overpotential and ohmic overpotential. The cathode activation and concentration overpotentials are relatively small. Increasing the reaction temperature results in a greater decrease in anode activation overpotential than ohmic overpotential, despite the increase in CO formation from the reverse Boudouard reaction. The peak power density of the FBMCDCFC is 434.437 W m-2 when operated at 923 K and a gas flow rate of 30 mL min-1. The peak power density of the FBMCDCFC is greater with higher temperatures, where the peak increases to 584.802 W m-2 when operated at 1023 K. The peak power density is greater with lower gas flow rates, where the peak increases to 458.175 W m-2 at a gas flow rate of 25 mL min-1. The mathematical model can aid in optimizing the performance of FBMCDCFCs, such as how increasing the operating temperature favorably increases anode reaction kinetics and reduces ohmic resistances in the cell. Future work will focus on improving the model correlations to close the gap between the results of modeling and actual experiments.Figure 1. a) Power curves at different temperatures, 823 K to 1323 K (30 mL min-1 flow rate, 1 atm total pressure); b) Power curves at different gas (O2 and CO2) flow rates (923 K, 1 atm total pressure) Figure 1

The role of reverse Boudouard reaction during integrated CO2 capture and utilisation via dry reforming of methane

Integrated carbon capture and utilisation (ICCU) is an emerging technology for simultaneous CO2 adsorption and conversion into value-added products. This provides a more sustainable approach compared to carbon capture and storage. Dual-functional materials (DFMs) that couple CO2 sorbents (e.g. CaO) and catalysts (e.g. Ni) enable direct utilisation of sorbed CO2 for reactions like dry reforming of methane (DRM). However, the potential interactions between sorbent and catalyst components within DFMs may induce distinct mechanisms compared to individual materials. Elucidating these synergies and interfacial phenomena is vital for guiding the rational design of DFMs. This article investigates the respective roles of Ni/SiO2 catalyst and sol–gel synthesised CaO sorbent in integrated CO2 capture and utilisation via dry reforming of methane (ICCU-DRM) using a decoupling approach. Through decoupled reactor experiments, it is found that Ni/SiO2 activates CO2 to react with carbon deposits from CH4 decomposition, achieving maximal CO and H2 yields of 43.41 mmol g−1 and 46.78 mmol g−1 as well as 87.2 % CO2 conversion at 650 °C. Characterisation shows that coke would encapsulate Ni nanoparticles and be active for CO2 conversion via Boudouard reaction, indicating sufficient catalyst-sorbent contact is necessary for CO2 spillover. In-situ DRIFTS reveals that no obvious CH4-CaCO3 reaction occurs, CO2 chemisorption on Ni/SiO2 enables the reverse Boudouard reaction, which is further verified by DFT calculations. The findings elucidate the dependent and synergistic roles of Ni/SiO2 and CaO/CaCO3 in ICCU-DRM, and highlight the importance of catalyst-adsorbent interactions in optimising dual-functional materials.

High efficiency electricity and gas cogeneration through direct carbon solid oxide fuel cell with cotton stalk biochar

For the first time, biochar derived from a renewable resource, cotton stalk, is used as the feedstock of direct carbon solid oxides fuel cells (DC-SOFCs) for electricity and gas cogeneration. It turns out that the cotton stalk biochar has plenty of naturally grown K and Ca, which are active catalysts for the reverse Boudouard reaction in DC-SOFCs. This natural advantage of the cotton stalk biochar enables an extremely high power density of an anode-supported DC-SOFC at 850 °C, 0.9 W cm−2, which is the highest among those of the reported DC-SOFCs. Meanwhile, high concentration of CO gas, which is an important feedstock for chemical industry, is obtained from the DC-SOFCs. The energy conversion efficiency of the electricity-gas cogeneration of DC-SOFCs reaches over 70%. A novel method, using compressed char, is proposed and carried out for continuous supply of cotton stalk char to a DC-SOFC. The present work has demonstrated the feasibility and advantages of cogenerating electricity and gas through DC-SOFCs with biochar derived from cotton stalk as the feedstock.

Chemical looping-based catalytic CH4 decomposition and successive coke gasification with CO2 on ordered mesoporous NiMCeOx (M = Co, Zr, La)

Highly ordered mesoporous NiLaCeOx mixed metal oxides were investigated as effective catalysts for the chemical looping-based dry reforming of methane (CH4) with carbon dioxide (CO2) (CL-DRM). This catalyst exhibited an excellent catalytic activity and stability in the decomposition of CH4 to form H2 with surface carbons subsequently activated by CO2 via reverse Boudouard reaction to form CO. Among the NiMCeOx catalysts with various promoter (M = Co, Zr, or La), the optimal NiLaCeOx catalyst preserved its original highly ordered mesoporous structures, leading to the higher dispersion of smaller Ni nanoparticles. This was attributed to the stronger Ni-Ce interactions facilitated by the La2O3 metal oxide promoter. The NiLaCeOx demonstrated a higher rate of H2 formation and successive CO production in the CL-DRM reaction, resulting in a H2/CO ratio above 1.0. Additionally, the NiLaCeOx catalyst exhibited superior structural stability over 5 cyclic CL-DRM reactions for CH4 decomposition (>85 %) and CO2 activation (>45 %), with minimal deposition of cokes.

Effect of Ni/SiO2 catalyst preparation method on methane decomposition and CO2 gasification cycles

Catalytic methane decomposition is a promising reaction to produce CO2-free hydrogen from methane-rich feedstock with solid carbon as a by-product. Significant research conducted on this reaction to find ways to manage and utilize this solid carbon. In this work, the methane decomposition reaction is followed by Reverse Boudouard Reaction using CO2 feedstock to convert the solid carbon to carbon monoxide, which is a valuable starting component for many chemical applications. Realizing this promising concept would require a catalyst that is efficient for both reactions. Herein, we explored the potential of using solution combustion synthesis (SCS) to make a 5 wt% of Ni supported SiO2 catalyst and benchmarked it versus the conventional impregnation method. The catalyst prepared by SCS showed an improved performance at different temperatures, space velocities, and catalyst pellet sizes. The SCS catalyst successfully completed five repeated cycles reaching up to 38.1 h of stable time on stream operation, whereas the impregnated catalyst was not able to complete the second testing cycle with only 14 h of time on stream operation. A thorough characterization using XRD, H2 and O2 TPR, TEM, SEM, XPS, and Raman spectroscopy were conducted to provide an adequate explanation for the observed performances for both catalysts. The Ni nanoparticles size and distribution, the strength of the metal support interaction, and the nature of graphitic carbon were the key factors affecting the catalytic performance. Insights on how to make an optimal catalyst for this promising process is identified which is a step forward toward making separated H2 and CO streams from methane feedstock and CO2, respectively.

Innovative application of tomato straw biochar in direct carbon solid oxide fuel cells for power generation

Direct carbon solid oxide fuel cells (DC-SOFCs) demonstrate significant promise in clean energy conversion technology due to their direct utilization of solid carbon, high-temperature operation, and fuel flexibility. Exploring biomass as a fuel for DC-SOFCs is particularly intriguing within this context. Here, we successfully developed the biochar derived from tomato straw and conducted a comprehensive physicochemical characterization to investigate its feasibility and advantages for DC-SOFCs. Electrochemical results revealed that DC-SOFC powered by tomato straw biochar achieved an impressive output of 219 mW cm−2 at 850 °C, surpassing the cell output of 187 mW cm−2 operating on commercial activated carbon. Furthermore, the single cell demonstrated a higher discharge plateau and a longer lifetime of 26.5 h under 50 mA at 850 °C. Consequently, fuel utilization was calculated to be up to 29.7%, which was also superior to that of activated carbon-fueled DC-SOFC, further validating the effectiveness of tomato straw biochar in improving DC-SOFC performance. These outstanding performances were primarily attributed to the unique porous microstructure, naturally existing metal elements, high disorder and large specific surface area of the biochar, which effectively promoted the reverse Boudouard reaction to produce a substantial amount of CO for anode reaction, thus enhancing the DC-SOFC performance and efficiency. These findings underscore the enormous application potential of tomato straw biochar for DC-SOFCs, providing strong support for advancing clean energy technology and achieving carbon neutrality goals.

Long-term evaluation of palm oil mill effluent (POME) steam reforming over lanthanum-based perovskite oxides

To replace the obsolete ponding system, palm oil mill effluent (POME) steam reforming (SR) over net-acidic LaNiO3 and net-basic LaCoO3 were proposed as the POME primary treatments, with promising H2-rich syngas production. Herein, the long-term evaluation of POME SR was scrutinized with both catalysts under the optimal conditions (600 °C, 0.09 mL POME/min, 0.3 g catalyst, & 74–105 μm catalyst particle size) to examine the catalyst microstructure changes, transient process stability, and final effluent evaluation. Extensive characterization proved the (i) adsorption of POME vapour on catalysts before SR, (ii) deposition of carbon and minerals on spent SR catalysts, and (iii) dominance of coking deactivation over sintering deactivation at 600 °C. Despite its longer run, spent LaCoO3 (50.54 wt%) had similar carbon deposition with spent LaNiO3 (50.44 wt%), concurring with its excellent coke resistance. Spent LaCoO3 (6.12 wt%; large protruding crystals) suffered a harsher mineral deposition than spent LaNiO3 (3.71 wt%; thin film coating), confirming that lower reactivity increased residence time of reactants. Transient syngas evolution of both SR catalysts was relatively steady up to 4 h but perturbed by coking deactivation thereafter. La2O2CO3 acted as an intermediate species that hastened the coke removal via reverse Boudouard reaction upon its decarbonation. La2O2CO3 decarbonation occurred continuously in LaCoO3 system but intermittently in LaNiO3 system. LaNiO3 system only lasted for 13 h as its compact ash blocked the gas flow. LaCoO3 system lasted longer (17 h) with its porous ash, but it eventually failed because KCl crystallites blocked its active sites. Relatively, LaCoO3 system offered greater net H2 production (72.78%) and POME treatment volume (30.77%) than LaNiO3 system. SR could attain appreciable POME degradation (>97% COD, BOD5, TSS, & colour intensity). Withal, SR-treated POME should be polished to further reduce its incompliant COD and BOD5.

CO2-assisted propane dehydrogenation to aromatics over copper modified Ga-MFI catalysts

The acidity and Ga-species status in the zeolite play a crucial role in the CO2-assisted propane dehydroaromatization (CO2-PDA). In this work, a copper modified Ga-MFI zeolite (Cu/Ga-MFI) with well dispersed framework Ga species was fabricated. A remarkable aromatics selectivity of 73% at propane conversion of 93.6% was achieved on Cu/Ga-MFI catalyst. The Ga atoms in MFI framework can create a moderate acid strength, while the introduced Cu provide an appropriate Brønsted/Lewis acid distribution, enhancing the synergy between metal-related species and the zeolite. Besides, DFT results indicate that the acid sites in Ga-MFI are more preferable for the dehydrogenation of propane instead of the C-C cleavage. Moreover, CO2 can inhibit coke formation through reverse Boudouard and reverse water gas shift reaction, which endows Cu/Ga-MFI catalyst with superior anti-coking ability and regeneration stability. This work provides a novel approach for designing catalysts with high activity, aromatics selectivity, and stability for CO2-PDA reactions.

Methane conversion to syngas by chemical looping on La0.8Sr0.2FexCo1-xO3 (x = 0, 0.25, 0.50, 0.75) perovskites with CO2 co-feeding

Partial oxidation of methane (POM) by chemical looping with CO2 co-feeding on La0.8Sr0.2FeO3 (LSF) perovskite catalyst yielded a highly selective operation and enabled to extend the duration of reduction cycle. In this work, the conversion of methane to syngas was studied on La0.8Sr0.2Fe(x)Co(1-x)O3 (x = 0, 0.25, 0.5, 0.75) perovskites in chemical-looping mode, co-feeding CO2 and methane. The reaction was conducted at 850 °C, 15 min reduction (10% methane in N2, 0–3% CO2), and 10 min oxidation (10% O2 in N2) cycles. The perovskites activity decreased with increasing Co content, in the absence of CO2, due to intensified coke deposition on the catalyst. Addition of CO2 during the reduction step (1–3%) reduced coke accumulation. A run conducted on La0.8Sr0.2CoO3 (LSC) with continuous feeding of CO2 and periodical (on–off) methane feeding indicated that CO2 reacts with the accumulated coke in reverse-Boudouard reaction, increasing CO selectivity without affecting the methane conversion. XRD analysis of reduced Co-containing perovskites indicates a decreasing perovskite content. Metallic Co and La2O3 phases increased as the Co content in the fresh perovskite increased, increasing coke deposition. As the Co content increased, the process shifts from POM with oxygen replenishment (LSF) to cracking followed by reverse-Boudouard reaction (LSC).

Catalytic calcium-looping gasification of biochar with in situ CO2 utilization with improved energy efficiency

Capture and conversion of CO2 from optimal-scenarios into fuels or chemicals provide a viable solution to combat climate change in reducing greenhouse gas emissions. Here, we propose and experimentally demonstrate that synergistic integration (Catalytic calcium-looping (CaL) gasification of biochar) can realize the capture and in situ conversion of CO2. Thermodynamic and kinetic estimations, catalytic conversion and cyclic tests and microstructure characterizations showed that by using a mixture of limestone and K2CO3-impregnated biochar, calcination fully coupled with the reverse Boudouard reaction can shift thermodynamic equilibrium and simultaneously induce the synergetic catalysis between CaCO3 and K2CO3, allowing for accelerating decarbonation kinetics, enhancing CO yield and maintaining stable cyclic CO2 conversion at lower temperatures (850 °C), as compared to the individual CaL and gasification processes. Theoretical calculations further revealed that the activation energy barriers for the monatomic C-assisted CO2 dissociation were lower than its desorption energy for CO2 on the K-doped CaO surface, demonstrating superior conversion reactivity. Importantly, the process is demonstrated in terms of practical scalability using a renewable and cost-effective reductant (biochar), a cheap catalyst (K2CO3) and inexpensive natural CO2 sorbents (limestone and dolomite) in an energy-efficient manner, therefore opening a unique direction for net-negative emission for large CO2 stationary sources eliminating the need for sequestration.

Effect of low-loading of Ni on the activity of La0.9Sr0.1FeO3 perovskites for chemical looping dry reforming of methane

Methane dry reforming (MDR) is a very appealing process to bring back waste CO2 into the chemical production chain. Operating in chemical looping (CL) conditions allows to reduce deactivation by coke deposition and facilitates the use of concentrating solar energy to power this reaction. Perovskites have successfully applied as oxygen carriers for chemical looping, and those of the family La1−xSrxFeO3 having lower Sr content have showed high activity and cycling stability for MDR. To further enhance the performance of these oxygen carriers, in this work we evaluate the impact of dispersing Ni in low concentration (<1 mol %) on the performance of La0.9Sr0.1FeO3 for CL-MDR. Simple impregnation allows to distribute evenly the metal, which according to XPS is present as Ni2+ in the fresh material. CH4-TPR reveal that NiOx species are firstly reduced at around 650 ºC and they shift the onset of methane partial oxidation to lower temperatures with regards to the unmodified perovskite. However, during isothermal CL tests at 850 ºC, the presence of Ni does not modify much the syngas production during the methane reforming stage, although the H2/CO ratio increases with the presence of this metal. This indicates an increment in the contribution of methane cracking. In contrast, when feeding CO2, the generation of CO is greatly enhanced by the incorporation of Ni, particularly at a loading of 0.4 mol %, while higher metal concentration are slightly less effective. Higher CO generation is attributed to the promotion of reverse Boudouard reaction, which can remove the coke previously deposited in the methane reforming stage. Accordingly, the Ni/ La0.9Sr0.1FeO3 presents stable activity during several consecutive cycles.

Effects of Operating Parameters and Feed Gas Compositions on the Dry Reforming of Methane over the Ni/Al2O3 Catalyst

The effects of operating parameters such as reaction temperature, space velocity, and feed gas composition on the performance of the methane dry-reforming reaction (DRM) over the Ni/Al2O3 catalyst are systemically investigated. The Ni/Al2O3 catalyst, which is synthesized by conventional wet impregnation, showed well-developed mesoporosity with well-dispersed Ni nanoparticles. CH4 and CO2 conversions over the Ni/Al2O3 catalyst are dramatically increased as both the reaction temperature is increased, and space velocity is decreased. The feed gas composition, especially the CO2/CH4 ratio, significantly influences the DRM performance, catalyst deactivation and the reaction behavior of side reactions. When the CO2-rich gas composition (CO2/CH4 &gt; 1) was used, a reverse water gas shift (RWGS) reaction significantly occurred, leading to the consumption of hydrogen produced from DRM. The CH4-rich gas composition (CO2/CH4 &lt; 1) induces severe carbon depositions followed by a reverse Boudouard reaction, resulting in catalytic activity drastically decreasing at the beginning followed by a stable conversion. The catalyst after the DRM reaction with a different feed ratio was analyzed to investigate the amount and structure of carbon deposited on the catalyst. In this study, we suggested that the optimal DRM reaction conditions can achieve stable performances in terms of conversion, hydrogen production and long-term stability.

A study of refractory carbon deposits on Ni/Al2O3 catalysts for dry reforming of methane

AbstractWhen investigating carbonaceous species on a catalyst via temperature‐programmed techniques, both the nature of the carbons and the possibility of the catalytic reaction of carbonaceous species should be considered. Here we examined CH4 decomposition (carbon deposition from CH4) and the reverse Boudouard reaction (carbon elimination by CO2) on the Ni/Al2O3 catalyst using sequential temperature‐programmed experiments. Carefully considering both the location and characteristics of carbon deposits formed on the Ni/Al2O3 catalyst, we conclude that carbons located on the Al2O3 support are challenging to remove by CO2 regardless of their nature, indicating the importance of support activity in reducing carbon deposits. In this study, the incorporation of cesium (Cs) into Al2O3 shows no effect on the prevention of carbon deposition from CH4 but does show an enhancement of carbon removal via the reverse Boudouard reaction, resulting in less coke formation on the Ni/Cs doped Al2O3 catalyst than the Ni/Al2O3 catalyst by 17 % for the dry reforming of methane.

Efficient Performance of the Methane-Carbon Dioxide Reform Process in a Fluidized Bed Reactor

The reforming of methane with CO2 was carried out efficiently in a fluidized bed reactor at 973 K under atmospheric pressure, taking advantage of the nickel catalyst efficiency achieved with a bed of particulate fines. The fluidization operation was characterized by determining a minimum velocity of 3.11 × 10−3 ms−1 and higher velocities. The reactor worked with surface speeds of up to 1.84 × 10−2 ms−1, providing conversions from 45% to 51% and a syngas yield of 97%. The control base of the operation focused on the use of CO2 was established through the reaction steps assumed for the process, including methane cracking, reverse Boudouard reaction, and RWGS (reverse reaction of water gas-shift). The reactor designed to operate in two zones was able to simultaneously process surface reactions and catalyst regeneration using feed with 50% excess CO2 in relation to methane. Predictions indicating the production of syngas of different compositions quantified with the H2/CO ratio from 2.30 to 0.91 decreasing with space-time were validated with the results available for process design.

Carbon photochemistry: towards a solar reverse boudouard refinery

Carbon and carbon dioxide can be concurrently converted using light to carbon monoxide via the reverse-Boudouard reaction.

A high-performance direct carbon solid oxide fuel cell powered by barium-based catalyst-loaded biochar derived from sunflower seed shell

Direct carbon solid oxide fuel cell (DC-SOFC) is one of the most attractive thesises for clean and efficient utilization of solid carbon to produce electricity. According to the operating principle, DC-SOFC performance is closely associated with the carbon sources and catalysts of the reverse Boudouard reaction. Here, we report a high-performance DC-SOFC powered by the biochar derived from sunflower seed shell (SSS) with barium-based catalyst loaded. The physicochemical properties of the SSS biochar are characterized and analyzed detailly. The electrolyte-supported symmetrical SOFC fueled with the SSS biochar gives an output of 216 mW cm−2 at 850 °C, indicating a great potential of the SSS biochar for DC-SOFCs. More importantly, the best output of 265 mW cm−2 and open circuit voltage of 1.03 V are obtained from DC-SOFC operated on 5 wt% barium-loaded SSS biochar, which is comparable to the output of 273 mW cm−2 from the hydrogen-fueled SOFC at 850 °C with the identical configuration. The superiorities of the SSS biochar and barium-based catalyst are also reflected in the operation stability and fuel utilization of DC-SOFCs. The discharge platforms are stable and the longest lifetime is up to 28.0 h under 50 mA with the fuel utilization of 31.3%, which is very excellent and competitive. This work provides a new idea for the effective utilization of the SSS biochar and other biomass for DC-SOFCs.

Numerical investigation of the reaction kinetics of dry reforming of methane over the yolk–shell and single-atom alloy catalysts

Dry reforming of methane (DRM) over Ni-based supported catalysts has been widely studied due to Ni's low cost and high activity. Despite their excellent performance, side reactions such as methane decomposition and Boudouard reaction can cause severe coke formation leading to catalyst deactivation. Our recent work reported that both yolk–shell morphology and Pt-Ni interaction in single-atom-alloy (SAA) structures could maintain the DRM activity. However, the effect of morphology and Pt-Ni interaction could not be elucidated. In this work, we studied the reaction kinetics of DRM by proposing a detailed elementary reaction mechanism with 12 surface species and 17 elementary steps over the Ptx-NiCe@SiO2 and Pt0.25-NiCe/SiO2WI catalysts. Due to the different DRM activity over the wet-impregnated and yolk–shell structures, we examined multiple reaction models to explain the effect of morphology and Pt-Ni interaction on the DRM activity. Our results show that the reverse Boudouard reaction and dissociative adsorption of CO2 and CH4 are the rate-limiting steps. The desorption of CO* and H* is also critical to products yield and selectivity. Compared with Pt0.25-NiCe/SiO2WI catalyst, the C* removal followed by the fast CO* desorption is more favored on Pt0.25-NiCe@SiO2 SAA, suggesting the reverse Boudouard reaction prevents the catalyst deactivation by coking. The high O* and low H* coverages are observed on Pt0.25-NiCe@SiO2 SAA due to the confined yolk–shell morphology and enhanced Pt-Ni interaction in SAA structures, respectively. Both these effects can lead to facile C* removal in the Pt0.25-NiCe@SiO2 SAA catalyst leading to a stable DRM activity.

Promoting Propane Dehydrogenation with CO2 over the PtFe Bimetallic Catalyst by Eliminating the Non-selective Fe(0) Phase

Fine tuning the structure of bimetallic nanoparticles is critical toward understanding structure–activity relationships and further improving the catalytic performance in propane dehydrogenation (PDH). Excessive Fe species in the PtFe bimetallic catalysts promote carbon deposition leading to low propylene selectivity, and it remains challenging to synthesize well-defined PtFe catalysts while selectively eliminating the excessive Fe. Herein, we show that the formation of coke can be significantly inhibited by introducing CO2 into the PDH over PtFe catalysts, where CO2 effectively eliminates the active Fe(0) coking sites without changing the catalytic surface structure of the PtFe alloy. With a CO2/C3H8 feeding ratio of 0.20, the Pt1Fe7/S-1 catalyst shows the highest propylene production rate and decreased amount of coke from 18.8 to 1.0 wt % compared with dehydrogenation without CO2. X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe Mössbauer results indicate that it is the oxidation of excessive unalloyed Fe species during the CO2-PDH reaction, instead of the reverse Boudouard reaction (CO2 + C = 2CO), that significantly inhibits the carbon deposition. This work provides a promising strategy for tuning the structure of PtFe bimetallic catalysts under reaction conditions and improving the performance of the PDH reaction.